Polishing platen of chemical mechanical polishing apparatus and planarization method using the same

ABSTRACT

A polishing platen of a chemical mechanical polishing apparatus and a planarization method using the same are disclosed. The polishing platen is formed of a first plate connected to a second plate. By independently controlling a thermal expansion of the first and second plates, a shape of an upper surface of the platen can be controlled and selectively altered. This allows a more precise polishing process and formation of a more uniform wafer. In one embodiment, the first and second plates, each have a different thermal expansion coefficient.

[0001] This application claims the benefit, under 35 U.S.C. §119, of Korean Application No. P2001-064016 filed on Oct. 17, 2001, which is herein fully incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a chemical mechanical polishing apparatus, and more particularly, to a polishing platen of a chemical mechanical polishing apparatus and a planarization method using the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for improving uniformity in wafer thickness by using a thermal expansion coefficient of the polishing platen.

[0004] 2. Discussion of the Related Art

[0005] Generally, a wafer is treated with a series of repeated processes, such as photolithography, ionic diffusion, etching, chemical vapor deposition, and metallic deposition, ultimately resulting in the fabrication of a chip (e.g., a semiconductor device).

[0006] A metallic line structure with a fine pattern is formed on the wafer treated with the above-mentioned processes. In fact, as the semiconductor device becomes highly integrated and functionalized, a multi-layered line structure consisting of a plurality of metal line structures, insulating layers, and interlayer line structures is formed on the wafer.

[0007] Such multi-layered line structures require a technique for planarizing a wafer surface. This is because if a gap exists between the wafer and a mask located on the wafer a pattern formed on the wafer becomes irregular. When a plurality of different fine patterns are sequentially formed on a wafer, having an irregular shape, the fine patterns are improperly formed. For example, a projection lens will be unable to be focused correctly. Thus, a required fine pattern is not achieved because of a low accuracy of the focus.

[0008] Accordingly, the definition of fine patterns may be enhanced by an initial planarization process of the irregular block of the wafer. Generally, planarization is carried out through a polishing process of the wafer surface.

[0009] The planarization process may include a borophospho Silicate glass BPSG reflow method (whereby boron and phosphor are doped), a spin on glass SOG etch-back method, and a chemical mechanical polishing CMP method.

[0010] In the BSPG reflow method, a BSPG layer is deposited on a surface of a semiconductor substrate and then annealed. In the SOG etch-back method, an SOG layer is additionally deposited on an insulating layer having a circuit pattern layer. The SOG layer is then etched in order to enhance the degree of planarization.

[0011] In the CMP method, a wafer having a step difference is adhered onto a pad and polished by using a slurry. This method is advantageous in that an overall planarization process can be carried out at a low temperature. Recently, the method has been widely used for planarizing memory devices of 256 mega and 1 giga size. More specifically, in the CMP method, a pad and a slurry are used to polish the wafer. A polishing platen attached to the pad rotates while a head unit rotates and vibrates in order to provide constant pressure.

[0012] The wafer is mounted on the head unit by either surface tension or vacuum. Due to a load of the head unit and the applied pressure, the wafer surface comes into contact with the pad. A processing liquid (i.e., the slurry) flows through fine gaps (i.e., pores of the pad) formed between the two contacting surfaces thereof. In a mechanical removal process, abrasive particles of the slurry and surface embossed portions of the pad are used. In a chemical removal process, slurry chemistry is used.

[0013] In the CMP process, contact begins at an upper portion of a protruded part of the device due to the pressure between the pad and the wafer. Since the pressure is concentrated on this portion, a surface eliminating speed is increased. During the process, irregular blocks are evenly reduced throughout the entire wafer surface.

[0014] One of oxide (SiO₂), polysilicon, and metallic layer is polished. Herein, a combined solution of a chemical etchant (i.e., a basic or acidic solution) and an etchant (i.e., alumina or silica) is used as abrasive.

[0015] Basically, oxide layers and metallic layers are processed with the CMP process under an identical sequence and with identical equipment. However, different slurries are used in each of the processes.

[0016] In an oxide layer CMP process, a slurry (including substances such as colloidal silica dispersed in an alkaline solution (i.e., KOH)) is used as an abrasive. In a metallic CMP process, abrasive slurries, such as KlO₃ and AlO₃, are used.

[0017] Generally, after a CMP process, particles and slurries produced during the process are removed with a double-sided brush scrubber DDS. All particles and residue produced on an oxide layer can be removed by using the DDS. However, those on a metallic layer cannot be completely removed with the DDS only. Therefore, a later cleaning process is necessary in order to remove all remaining slurries, metallic impurities, and particles. For a cleansing solution, one of deionized water (DI water), NH₄OH H₂O₂:H₂O compositions (hereinafter, referred to as SC-1) and HF solution is used.

[0018] The related art CMP apparatus for fabricating a semiconductor device will now be explained with reference to the accompanying drawings. FIGS. 1 and 2 illustrate structures of a related art CMP apparatus for fabricating a semiconductor device. More specifically, FIG. 1 is a CMP apparatus with an air pressure applying method using air holes. FIG. 2 is a CMP apparatus with an air pressure applying method using an air membrane.

[0019] As shown in FIGS. 1 and 2, a pad 12 is attached to a polishing platen 11. A semiconductor wafer 14 is secured to a wafer carrier 13 and mounted on the pad 12. The semiconductor wafer 14 is secured to the wafer carrier 13 by means of either surface tension or vacuum.

[0020] The wafer carrier 13 rotates to cause friction with the pad 12. Thus, a surface of the semiconductor wafer 14 secured to the wafer carrier 13 is polished.

[0021] A lower portion of the wafer carrier 13 includes a wafer supporting layer (not shown) and a wafer supporting ring (not shown), which secures the semiconductor wafer 14.

[0022] In addition, a slurry 15 is supplied to the pad 12 in order to accurately polish the wafer 14. After polishing the semiconductor wafer 14, a cleansing solution is applied to the pad 12 in order to cleanse the pad 12 and the semiconductor wafer 14 and to prepare them for subsequent processes.

[0023] In the related art CMP apparatus, air pressure 16, supplied through air holes (as shown in FIG. 1) or a membrane 17 (as shown in FIG. 2), is applied to a portion of the wafer carrier 13, whereby the semiconductor wafer 14 is secured during the CMP process. Thus, air pressure is applied to the back side of the wafer during polishing of the semiconductor wafer 14.

[0024] The polishing platen 11 is formed of metals that are highly resistant to corrosive conditions, such as stainless steel or aluminum.

[0025] More specifically, the related art CMP apparatus polishes a semiconductor wafer by applying air pressure 16, through air holes or a membrane 17, to the back side of the wafer, thereby planarizing the wafer.

[0026] However, the related art CMP has the following disadvantages. When the air pressure is increased to a level exceeding a set range, the wafer is pushed out of the wafer carrier, causing the wafer to break.

[0027] In addition, using air pressure may have some limitations. It is impossible to increase polishing pressure on a specific region only. In other words, an almost equal amount of pressure is applied to the overall wafer, which prevents an effective control of wafer uniformity.

SUMMARY OF THE INVENTION

[0028] Accordingly, the present invention is directed to a polishing platen of a chemical mechanical polishing apparatus, and a planarization method using the same, that substantially obviates one or more problems due to limitations and disadvantages of the related art.

[0029] An object of the present invention is to provide a polishing platen of a chemical mechanical polishing apparatus, and a planarization method using the same, that can enhance wafer uniformity during a CMP process by using a thermal expansion coefficient of a metallic material that forms the polishing platen.

[0030] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof, as well as the appended drawings.

[0031] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a polishing platen of a chemical mechanical polishing (CMP) apparatus, which supports a pad holding a semiconductor wafer that rotates during a CMP process, includes an upper metallic plate, and a lower metallic plate, each having a different thermal expansion coefficient.

[0032] In another aspect of the present invention, a planarization method of a CMP apparatus, which adsorbs under a state of vacuum a semiconductor wafer onto a pad using a wafer carrier, and which polishes a semiconductor wafer surface by rotating the wafer carrier and by causing friction between the pad and the semiconductor wafer using air pressure or a membrane, includes attaching to a lower portion of the pad a polishing platen. The platen is formed of an upper metallic plate and a lower metallic plate, each having a different thermal expansion coefficient. The method includes polishing the semiconductor wafer by applying different temperatures to the upper metallic plate and the lower metallic plate and by supplying a slurry on the pad, and supplying a cleansing solution on the pad in order to cleanse the pad and the semiconductor wafer after the polishing process of the semiconductor wafer.

[0033] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings:

[0035]FIGS. 1 and 2 illustrate a chemical mechanical polishing (CMP) apparatus for fabricating a semiconductor device, in accordance wit the related art;

[0036]FIG. 3 illustrates a state of a polishing platen of a CMP apparatus, according to the present invention before processing begins;

[0037]FIGS. 4A and 4B and FIGS. 5A and 5B are cross-sectional views illustrating the varying shapes of the polishing platen of the CMP apparatus, according to the present invention and controlling principles to attain wafer uniformity; and

[0038]FIG. 6 is a perspective view illustrating a structure of the polishing platen of the CMP apparatus, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0040] The present invention provides a polishing platen which has a shape that can be controllably varied. The platen can be used in a CMP apparatus identical to that of the related art. The inventive platen includes two metallic plates of different thermal expansion coefficients attached to each another. By controlling a temperature of the upper and lower metallic plates of the polishing platen during a CMP process of the semiconductor wafer, the polishing platen's shape is modified. Thereby, the present invention allows an edge or middle portion of the semiconductor wafer to be selectively polished more aggressively.

[0041] More specifically, as shown in FIGS. 1 and 2, the CMP apparatus includes a semiconductor wafer 14 adsorbed under a state of vacuum onto a pad 12 by means of a wafer carrier 13. While the wafer carrier 13 rotates oscillates or otherwise moves, the pad 12 and the semiconductor wafer 14 produce friction by using air pressure 16 or a membrane 17 to polish a surface of the semiconductor wafer 14.

[0042] The polishing platen 11, onto which the pad 12 is attached includes a first or an upper metallic plate and a second or lower metallic plate. The plates have different thermal expansion coefficients. Thus, a polishing process concentrated on a central or edge portion of the semiconductor wafer can be carried out in accordance with a difference in temperature.

[0043]FIG. 3 illustrates a state before processing with a polishing platen of a CMP apparatus, according to the present invention. As shown in FIG. 3, an upper metallic plate 20 and a lower metallic plate 30, having different thermal expansion coefficients, are attached to one another to form the polishing platen. The upper metallic plate 20 and the lower metallic plate 30 may be attached by an adhesive or a screw.

[0044] The upper metallic plate 20 has a thermal expansion coefficient higher than that of the lower metallic plate 30, or vice versa. For example, stainless steel or aluminum may be used as the upper metallic plate 20, and cast iron may be used as the lower metallic plate 30, or vice versa.

[0045]FIGS. 4A and 4B and FIGS. 5A and 5B are cross-sectional views illustrating modified shapes of the polishing platen of the CMP apparatus, according to the present invention. The FIGs. also illustrate controlling principles to attain wafer uniformity during polishing.

[0046] As shown in FIG. 4A, the above-described polishing platen includes an upper metallic plate 20 having a thermal expansion coefficient higher than that of a lower metallic plate 30. Therefore, as shown in FIG. 4B, the polishing platen curves upwards into a convex shape, when the lower metallic plate 30 is set at a low temperature relative to the upper metallic plate 20.

[0047] Conversely, as shown in FIG. 5A, the polishing platen includes a lower metallic plate 30 having a thermal expansion coefficient higher than that of an upper metallic plate 20. Therefore, as shown in FIG. 5B, the polishing platen curves downwards into a concave shape, when the upper metallic plate 20 is set at a low temperature relative to the lower metallic plate 30.

[0048] When the polishing platen of the CMP apparatus curves into a convex shape, as shown in FIG. 4B, polishing pressure increases at the central portion of the semiconductor wafer 40. Therefore, a removal rate at the central portion of the semiconductor wafer 40 is increased relative to a removal rate at the edge portions of the semiconductor wafer 40.

[0049] Conversely, when the polishing platen of the CMP apparatus curves into a concave shape, as shown in FIG. 5B, polishing pressure increases at the edge portions of the semiconductor wafer 40. Therefore, a removal rate at the edge portions of the semiconductor wafer 40 is increased relative to a removal rate at the central portion of the semiconductor wafer 40.

[0050] A heating line and a cooling line are embedded within the upper metallic plate 20 and the lower metallic plate 30, thereby enabling accurate control of temperatures therein. During the CMP process of the semiconductor wafer, a difference in temperature is controlled between the upper metallic plate 20 and the lower metallic plate 30 of the polishing platen, thereby changing the shape of the polishing platen. Thus, the polishing pressure can be controlled at the central and edge portions of the semiconductor wafer. This control results in better uniformity of the wafer during the polishing process.

[0051] For example, if the temperature of the upper metallic plate 20 is increased and the temperature of the lower metallic plate is decreased, the polishing platen turns into a convex shape (FIG. 4B). This shape causes the polishing pressure of the central portion on the semiconductor wafer to increase during the polishing process, thereby causing an increase in a removal rate at the central portion of the wafer.

[0052] Conversely, if the temperature of the upper metallic plate 20 is decreased and the temperature of the lower metallic plate 30 is increased, the polishing platen turns into a concave shape (FIG. 5B). This shape causes the polishing pressure on the edge portions of the semiconductor wafer to increase during the polishing process, thereby causing an increase in a removal rate at the edge portions of the wafer.

[0053] After the polishing process, a cleansing solution is applied to the semiconductor wafer for cleansing. The cleansing solution prepares the wafer for further processing.

[0054]FIG. 6 is a perspective view illustrating a structure of the polishing platen of the CMP process, according to the present invention. As shown in FIG. 6, a heating line and a cooling line 50 are embedded within the upper metallic plate 20 and the lower metallic plate 30. This arrangement enables unrestricted control of temperatures in the upper and lower metallic plates 20, 30.

[0055] As described above, the polishing platen of the CMP apparatus, and the planarization method using the same, have several advantages. Unlike the related art apparatus, polishing pressure can be controlled at a surface which comes into contact with a front side of the wafer. This improves uniformity of the wafer after polishing.

[0056] In addition, the present invention uses a thermal expansion coefficient. Thus, the structure of the apparatus is simpler than an apparatus using air pressure, and the polishing pressure can be controlled more accurately.

[0057] In an apparatus whereby air pressure is applied to a back side of the wafer in order to control wafer uniformity, the wafer may be pushed outside the wafer carrier when excess air pressure is applied. However, in the present invention, such risk can be avoided.

[0058] Although a single heating and cooling line 50 is depicted in each of the upper and lower plates 20, 30, it is envisioned that each plate could contained one line dedicated for heating and one line dedicated for cooling. A heating or cooling line could be an electrical wire, (e.g. a resistive heating wire), or a conduit. In the case of a conduit, a temperature controlled gas or fluid could be passed through the line to control the temperature of the respective plate 20 or 30.

[0059] Since the upper plate 20 has a different thermal expansion coefficient than the lower plate 30, it is possible to cause a deformation on the upper surface of the upper plate 20 by controlling a common temperature to both the upper and lower plate. For example, if the upper plate 20 is formed of stainless steel and the lower plate 30 is formed of cast iron, a deformation of the upper platen will occur as the upper and lower plates incur a common temperature change.

[0060] Furthermore, it is possible to form the upper and lower plates 20, 30 of a same material having a same thermal expansion coefficient. In this arrangement, if a temperature of the upper plate 20 is controlled (via a heating or cooling line) to be different than a temperature of the lower plate 30 (via a different heating or cooling line), the upper surface of the upper platen will be controllably deformed. However, in a preferred embodiment of the present invention, it can be observed that by forming the upper plate 20 of a material having a different thermal expansion coefficient than the lower plate 30, and by additionally controlling a temperature differential between the upper and lower plates 20, 30, that the deformation will be more pronounced.

[0061] It will be apparent to those skilled in the art than various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

What is claimed is:
 1. A polishing platen of a chemical mechanical polishing apparatus, which apparatus moves a semiconductor wafer relative to said polishing platen to accomplish a chemical mechanical polishing process on the wafer, said polishing platen comprising: an upper metallic plate having a first thermal expansion coefficient; and a lower metallic plate having a second thermal expansion coefficient, different than said first thermal expansion coefficient.
 2. The polishing platen of claim 1, further comprising: at least one of a heating line and a cooling line embedded in at least one of said upper metallic plate and said lower metallic plate.
 3. The polishing platen of claim 1, further comprising: a heating and cooling line embedded in at least one of said upper metallic plate and said lower metallic plate.
 4. The polishing platen of claim 1, further comprising: a first heating and cooling line embedded in said upper metallic plate; and a second heating and cooling line embedded in said lower metallic plate.
 5. The polishing platen of claim 1, wherein said first thermal expansion coefficient is greater than said second thermal expansion coefficient.
 6. The polishing platen of claim 1, wherein said first thermal expansion coefficient is less than said second thermal expansion coefficient.
 7. The polishing platen of claim 1, wherein said upper metallic plate is formed of either stainless steel or aluminum.
 8. The polishing platen of claim 7, wherein said lower metallic plate is formed of cast iron.
 9. The polishing platen of claim 1, wherein said lower metallic plate is formed of either stainless steel or aluminum.
 10. The polishing platen of claim 9, wherein said upper metallic plate is formed of cast iron.
 11. The polishing platen of claim 1, wherein said upper metallic plate and said lower metallic plate are attached by an adhesive or a screw.
 12. A polishing apparatus comprising: a platen; a pad supported on said platen; a holder for positioning a semiconductor wafer adjacent to said pad; and a drive connected to at least one of said platen and said holder causing relative movement between said holder and said pad to polish the semiconductor wafer, wherein said platen includes: a first plate having a first thermal expansion coefficient; and a second plate having a second thermal expansion coefficient, different than said first thermal expansion coefficient.
 13. The polishing apparatus of claim 12, further comprising: at least one of a heating line and a cooling line embedded in at least one of said first plate and said second plate.
 14. The polishing apparatus of claim 12, further comprising: a first heating or cooling line embedded in said first plate; and a second heating or cooling line embedded in said second plate.
 15. The polishing apparatus of claim 12, wherein: said first plate includes a first side and an opposite, second side; said second plate includes a first side and an opposite, second side; said first side of said second plate is attached to said second side of said first plate; said first plate is formed of a metal having said first thermal expansion coefficient; and said second plate is formed of a metal having said second thermal expansion coefficient.
 16. The polishing apparatus of claim 15, wherein said first surface of said first plate assumes a convex or concave shaped depending upon a temperature of said first and second plates.
 17. The polishing apparatus of claim 15, wherein one of said first and second plates is formed of stainless steel or aluminum, and the other of said first and second plates is formed of cast iron.
 18. The polishing apparatus of claim 15, wherein said first surface of said second plate is attached to said second surface of said first plate by an adhesive or a screw.
 19. A polishing apparatus comprising: a platen; a pad supported by said platen; a holder for positioning a semiconductor wafer adjacent to said pad; and a drive connected to at least one of said platen and said holder causing relative movement between said holder and said pad to polish the semiconductor wafer, wherein said platen includes: a first plate having a first surface and an opposite, second surface; a second plate having a first surface and an opposite, second surface, wherein said first surface of said second plate is attached to said second surface of said first plate; a first heating or cooling line controlling a temperature of said first plate; and a second heating or cooling line controlling a temperature of said second plate, to thereby cause said first surface of said first plate to assume a convex or concave configuration based upon a temperature differential between said first and second plates.
 20. The polishing apparatus of claim 19, wherein one of said first and second plates is formed of stainless steel or aluminum, and the other of said first and second plates is formed of cast iron.
 21. The polishing apparatus of claim 19, wherein said first surface of said second plate is attached to said second surface of said first plate by an adhesive or a screw.
 22. A planarization method of a chemical mechanical polishing apparatus comprising: providing a platen formed by the attachment of a first plate and a second plate; providing a pad on the platen; engaging a wafer to a surface of the pad; causing relative movement between the wafer and the surface of the pad to polish the wafer; and controlling a temperature of at least one of the first and second plates to cause platen, and hence the surface of the pad, to adjust to a desire shape to influence the polishing of the wafer.
 23. The method according to claim 22, further comprising: applying a slurry on the surface of the pad.
 24. The method according to claim 22, wherein a temperature of the first plate is elevated relative to a temperature of the second plate to enhance polishing of a central portion of the wafer.
 25. The method according to claim 22, wherein a temperature of the second plate is elevated relative to a temperature of the first plate to enhance polishing of edge portions of the wafer. 